1. Field of the Invention
The present invention relates to a current sensor structure that employs a molding compound for prevention of deformation of a core secured in a case, the core deformation being caused by dilation and contraction of the case.
2. Description of the Related Art
A number of state of the art current sensor configurations are advocated that are incorporated in an electrical junction box provided in automobiles and hybrid automobiles. For example, Japanese Patent Application Laid-Open Publication No. 2009-222729 discloses a current sensor in which a rectangular and ring-shaped metal magnetic core, which has a notch portion and takes a non-continuous appearance, is accommodated in a case made of insulating synthetic resin. A hall element is arranged in the notch portion of the core. A busbar made of conductive metal is passed through the core.
A space defined by an outer circumferential surface of the core and an inner circumferential surface of the case is filled with an insulating molding compound so that the core is secured to the case. A magnetic field caused by a current flowing through the busbar is amplified by the presence of the core and is detected by the hall element.
A positioning projection is provided on the inner circumferential surface of the case in the radial direction. The positioning projection is adapted to be brought into abutment on an outer circumferential surface of the core in the radial direction for prevention of position gap of the core while filling of the molding compound (see FIGS. 1 to 3).
Japanese Patent No. 4,418,332 discloses another known current sensor that employs a hall element. A wiring harness is passed through a core and secured to a case using a band. Power is supplied via a connector portion of the case, and the detected voltage is output on the same connector portion (see FIGS. 1 and 2).
In such current sensors of state of the art configurations as disclosed in the No. 2009-222729 document, the projection formed on the inner surface of the case is brought into abutment on the outer circumferential surface of the core in the radial direction, and this abutment structure facilitates prevention of the core getting out of position due to pressure in the course of filling of the molding compound. Since the surface of the core in its thickness direction is adhered and secured to the inner surface of the wall portion of the front side of the case via the thick-walled molding compound, the core stress in the direction of the case's dilation and contraction acts upon the core via the thick-walled molding compound as the case experiences dilation and contraction due to rapid change in temperature and humidity (i.e., the case's dilation and contraction causes the stress to act upon the core). As a result, the shape of the core changes, which in turn causes decrease in output and accuracy in current sensing.